Modern wind turbines are capable of generating a considerable amount of electric power. They typically have power ratings of several megawatts. The electric power generated by the wind turbine is generally raised to a higher voltage level (usually a medium-voltage level) which is more suitable for transmission, via a transformer which is associated with the wind turbine (turbine transformer). For protecting the wind turbines and the grid, circuit breakers are required on both sides of the turbine transformer. In this case, it is problematic that the circuit breakers on the low-voltage side of the turbine transformer have quite high currents. In the case of the wind turbine power levels of several megawatts which are now being achieved, this sometimes makes expensive special designs necessary for the circuit breakers.
Various ways have been proposed to make it possible nonetheless to manage sufficiently large currents. A first way would be to increase the voltage level on the low-voltage side, in order thereby to lower the current load. However, this has proven to be impractical due to the upper limits for voltages which are defined in relevant standards; thus, they still fall into the low-voltage range. The limit values (1000 VAC) are already being strained. A second way could be simply to connect two circuit breakers in parallel. This internal proposal by the applicant may provide the advantage that during normal operation, each of the two circuit breakers has to accommodate only half the amperage. However, this has proven to be insufficiently operationally reliable in the case of switchover. Due to structural tolerances, it is practically unavoidable that one of the two circuit breakers switches faster than the other; thus, in the interim, the entire current flows via only a single circuit breaker. This circuit breaker thereby becomes overloaded. This problem has a particularly unfavorable effect in the case of a short circuit, if the highest current load occurs. As a result, this means that precisely in the situation when the circuit breakers are needed (for example, in a short circuit), there is a high probability that they will fail due to overloading. This is unsatisfactory.